UHT Cartons of milk!!! Very popular in hotels and guest houses, we hate them. They are messy, they make tea taste weird and all that plastic has to be bad for the environment.
Even worse, many hotels seem to ration them, two per guest, so if you want more than 1 drink in your room (as it normally takes two to make a descent drink) you have to ask for more.
That's why all the Pottery House guest rooms have a mini-fridge with your own bottle of fresh milk for tea and coffee.